Here’s a news flash for anyone who may be unfamiliar with this newfangled thing called the Internet: there’s pornography on it. There’s even an often-invoked protocol courtesy of raunchy online message boards like 4Chan, knowns as Rule 34: “If it exists, there is porn of it.”

So it’s hardly surprising that just four days after its launch, Vine, Twitter’s new microvideo blogging service, is battling a flesh-toned scourge. Monday morning, Vine users who opened their iPhone app found an explicit video at the top of their Editor’s Picks feed. The video’s content should have been no surprise to editors, as it was tagged prominently with “nsfw,” “porn,” and “nsfwvine.” The video, featuring a woman and a sex toy, appeared at the top of Vine’s main screen, which is what all users see by default when they open the app.

It’s hard to tell if the video played immediately – as most Vine videos do – because it was quickly put behind a “sensitive content” filter. In a statement released quickly after the video was taken down Monday, Twitter said:

“A human error resulted in a video with adult content becoming one of the videos in editor’s picks, and upon realising this mistake we removed the video immediately. We apologise to our users for the error.”

Around 10 a.m. Eastern time, the video was removed from the Editor’s Picks section after being featured for a few hours. Vine’s app isn’t age-restricted and doesn’t even have a ban on nudity its Terms of Service, WebProNews reports, although it does ban “impersonation, spam, abuse, harassment and copyright infringement.”

While it’s safe to say that the only time you’ll see porn on Vine is if you’re looking for it, many users are outraged that the service is having trouble curbing the graphic videos. The “sensitive content” filter isn’t slapped over a video until it’s actually flagged as inappropriate by a user, and even then, it’s pretty simple to view the graphic content – a quick tap of the screen will show the video.

Vine, which allows users to create videos lasting six seconds or less and post them on social media, was launched last Thursday to widespread fanfare – and complaints. New adopters looking to share their videos on Twitter and Facebook found that feature unavailable just hours after the launch, leading many to speculate that Facebook had blocked Vine for its users. (The cross-posting service was restored within a few hours.) Some users also complained that their videos were being posted to other users’ accounts.

Critics and supporters alike are worried for the app’s future in the iTunes store. Apple, which famously polices pornographic content in its apps, pulled the popular 500px photography app last week amid complaints that the app made it too easy to find nude photos.

Vine’s tagline is “make a scene” – words that never felt more appropriate than they do now.